Improve bloom effect (#12916)

* Remove the built-in exposure factor of 2.5
* Add physics-based bloom (https://learnopengl.com/Guest-Articles/2022/Phys.-Based-Bloom)
* Add luminance scaling for bloom layer to simulate HDR
* Add setting to control bloom strength

1 files changed, 10 insertions, 4 deletions

diff --git a/client/shaders/extract_bloom/opengl_fragment.glsl b/client/shaders/extract_bloom/opengl_fragment.glsl
index 7d18ec26f..af320f9ab 100644
--- a/client/shaders/extract_bloom/opengl_fragment.glsl
+++ b/client/shaders/extract_bloom/opengl_fragment.glsl
@@ -2,7 +2,7 @@
 
 uniform sampler2D rendered;
 uniform mediump float exposureFactor;
-uniform float bloomLuminanceThreshold;
+uniform mediump float bloomStrength;
 
 #ifdef GL_ES
 varying mediump vec2 varTexCoord;
@@ -14,8 +14,14 @@ centroid varying vec2 varTexCoord;
 void main(void)
 {
 	vec2 uv = varTexCoord.st;
-	vec4 color = texture2D(rendered, uv).rgba;
+	vec3 color = texture2D(rendered, uv).rgb;
 	// translate to linear colorspace (approximate)
-	color.rgb = pow(color.rgb, vec3(2.2)) * exposureFactor;
-	gl_FragColor = vec4(color.rgb, 1.0); // force full alpha to avoid holes in the image.
+	color = pow(color, vec3(2.2));
+
+	// Scale colors by luminance to amplify bright colors
+	// in SDR textures.
+	float luminance = dot(color, vec3(0.213, 0.515, 0.072));
+	luminance *= luminance;
+	color *= luminance * exposureFactor * bloomStrength;
+	gl_FragColor = vec4(color, 1.0); // force full alpha to avoid holes in the image.
 }